Optical measurements are commonly used to characterize and measure materials including the biological properties of such materials. In these measurements, directed optical radiation (such as from lasers or light emitting diodes) is directed onto a sample of material. Some of the radiation changes after it strikes, or passes through, the biological material. Analysis is then performed on light (fluorescence) emitted from the sample in order to determine its properties.
Many biological materials fluoresce. Fluorescence is technically emission at one wavelength after a material absorbs light of another wavelength. The emitted wavelength is longer (lower frequency) than the absorbed light. Fluorescence properties are often used in biological measurements in order to denote the presence or absence of specific molecules. In a typical example, a sample material is illuminated by incident radiation of a particular frequency, and fluorescent light of a different frequency is detected and measured. The ratio of fluorescent light to incident radiation is typically small (e.g., one part in 108 to one part in 1012). A filter is therefore used to block incident radiation (often called the pump light) reflected from the sample material to prevent saturation of the detector (e.g., camera). Since the amount fluorescent light compared to the pump light is very small, the filter must pass substantially all light at the wavelength of the expected fluorescence and also block substantially all light at the wavelength of the pump light. In certain cases, biological properties of the sample material are measured over an area of the sample, and not just at one small portion of the sample material; this complicates set-up and data measurement.
A paper titled “Surgery with molecular fluorescence imaging using activatable cell-penetrating peptides decreases residual cancer and improves survival” by Q. T. Nguyen, et al., (PNAS, 107, (2010), 4317) describes one approach to measuring fluorescence and is incorporated herein by reference. However, the approach in this paper has the disadvantage in that the camera must have very low noise, as the fluorescent light from the sample material is very weak. Further, it is difficult to amplify the signal on the sensor without introducing additional noise. Typically, fluorescent light is captured over a long period, making the process more expensive.
By way of further background, a paper titled “The fabrication of fine lens arrays by laser beam writing” by M. T. Gale and K. Knop, (Proc. SPIE v. 398, page 347) describes exemplary scanning of a two dimensional stage and is incorporated herein by reference. Another paper titled “Generation of large-diameter diffractive elements with laser pattern generation” by John P. Bowen, Robert L. Michaels, and C. Gary Blough, (Applied Optics, Vol. 36, Issue 34, pp. 8970-8975 1997) discloses application of optical radiation to a sample and is likewise incorporated herein by reference.